SANTA ANA (AP) — Seven people sickened by E. coli in Orange County dined at the same Souplantation restaurant, health authorities said.

The seven who tested positive for the dangerous bacterium ate at a Souplantation in Lake Forest, six on March 23 or March 24, said Howard Sutter, spokesman for the county”s Health Care Agency. The seventh could not confirm an exact date.

Authorities have yet to determine the source. The restaurant was allowed to remain open after health inspectors concluded its food and conditions were safe, Sutter said.

Six of the seven sickened are children under age 18, said Tricia Landquist, a spokeswoman with the agency. The other person is in their 70s.

“Usually very young children or older adults with ongoing medical conditions already are more susceptible to developing a more severe form of this infection if it”s not treated early,” she said.

The seven cases were reported to county authorities in recent days. Three of those sickened were hospitalized, although their symptoms were not considered life-threatening, Sutter said.

Ken Keane, president of Souplantation”s parent Garden Fresh Restaurant Corp., said in a statement that the company was working with health officials to investigate the contamination source and “remain committed to the highest level of quality, cleanliness and service.”

“The health and welfare of our guests and employees is always our top priority,” Keane said.

Souplantations are serve-yourself salad-buffet restaurants.

E. coli can be found in the intestines of people and animals and is usually harmless, but can sicken people through various routes and to varying degrees, according to the Health Care Agency.

People can become infected if they eat contaminated food that is not cooked sufficiently to kill the bacteria. It can be passed from person to person if someone does not wash their hands properly after using the restroom or changing diapers. Symptoms usually start three to four days after exposure.